Have you ever tried FluxBox? I used to use OpenBox, but I just started using FluxBox last night and I love it to death. I used to use GNOME and KDE before that, and they were resource hungry monsters that ate up my processor time and RAM. I have 512 MB's of RAM, and I've actually had to hit swap a couple of times on GNOME. KDE is even worse.
From now on I'm just using Fluxbox.
